Protective tube for cryogenic applications

Abstract

The present invention relates to a protective tube (5) for a device (3) for determining and / or monitoring at least one process variable (T) of a medium (M) in a container (2), the protective tube comprising a tubular, in particular cylindrical, element (7) which is used to accommodate a measuring insert (4) of the device (3), and it being possible to fasten the tubular element (7) to the container (2) such that the tubular element (7) projects at least in part into an inner volume of the container (2). According to the invention, the tubular element (7) has an inlet opening (8) and an outlet opening (9), which inlet opening (8) and outlet opening (9) are situated on mutually opposite sides of the tubular element (7). The invention also relates to an arrangement (1) for determining and / or monitoring a process variable of a medium (M) in a container (2), the arrangement comprising: a device (3) for determining and / or monitoring the process variable by means of a measuring insert (4) which is used to determine and / or monitor the process variable; and a protective tube (5) according to the invention.

Description

[0001] The present invention relates to an arrangement comprising a container with a medium arranged therein and a device for determining and / or monitoring at least one process variable of the medium in the container, with a measuring insert that serves to determine and / or monitor the process variable, and with a protective tube. The container is, for example, a container or a pipeline.

[0002] Thermowells are used, for example, to insert measuring inserts of field devices into a container. These are used to determine and / or monitor one or more process variables, in particular physical or chemical ones, of a medium, in particular a fluid. These are generally immersion bodies that are at least partially immersed in the medium and are designed to accommodate the measuring insert. They have, for example, a central bore or a blind hole into which the measuring insert can be inserted. The thermowell then essentially functions as a housing. The thermowells themselves are typically inserted into a nozzle of the container or a measuring tube that can be integrated into a pipeline.

[0003] An exemplary application for thermowells in the field of field devices concerns thermowells, which are frequently used, especially in the case of invasive temperature determination, to protect a measuring insert containing the respective temperature sensor from the respective medium. Although the present invention is also applicable to other types of field devices, the following description refers to temperature measurement technology as an example.

[0004] Thermometers in a wide variety of designs have become known in the art, and their underlying measuring principles have also been described in detail. For example, there are thermometers that use the expansion of a liquid, gas, or solid with a known coefficient of expansion to measure temperature, or those that relate the electrical conductivity of a material to temperature, such as when using resistance elements or thermocouples. In contrast, radiation thermometers, especially pyrometers, utilize the thermal radiation of a substance to determine its temperature.

[0005] A temperature sensor in the form of a so-called thin-film sensor, particularly a resistance temperature detector (RTD), uses a sensor element provided with connecting wires and applied to a carrier substrate. The back of the carrier substrate is usually coated with metal. The sensor elements used are so-called resistance elements, which are provided, for example, by platinum elements, and are also commercially available under the designations PT10, PT100, and PT1000, among others.

[0006] With temperature sensors in the form of thermocouples, the temperature is determined by a thermoelectric voltage that develops between thermocouple wires made of different materials connected at one end. Thermocouples according to DIN standard IEC584, e.g., thermocouples of type K, J, N, S, R, B, T, or E, are typically used as temperature sensors. However, other material pairs, especially those with a measurable Seebeck effect, are also possible.

[0007] The accuracy of temperature measurement depends sensitively on the respective thermal contacts and the prevailing heat conduction. The heat flows between the medium, the container containing the medium, the thermometer, the thermowell, and the process environment all play a crucial role. For reliable temperature determination, it is important that the respective temperature sensor and the medium are essentially in thermal equilibrium for at least the period required to record the temperature.

[0008] In this context, it is advantageous if the temperature sensor is immersed in the respective medium via a protective tube, as this allows for a comparatively good coupling between the medium and the temperature sensor. However, depending on the temperature range of the medium and a temperature difference between the temperature of the medium and the ambient temperature, unwanted heat conduction from the medium to components located outside the process, or vice versa, can also occur via the measuring insert and protective tube. In both cases, the unwanted heat conduction leads to a heat dissipation error and thus to a significant reduction in measurement accuracy. This problem also particularly affects applications at cryogenic, i.e. low, temperatures.

[0009] The German patent application DE 25 49 619 A1 discloses an arrangement with a container and with a protective tube with an inlet opening and an outlet opening, which are arranged on opposite sides of the protective tube, so that the measuring insert is flowed around.

[0010] Japanese patent application JP 2002 310806 A also discloses an arrangement comprising a container and a protective tube with an inlet opening and an outlet opening arranged on opposite sides of the protective tube.

[0011] None of these arrangements are used in cryogenic applications.

[0012] The invention is based on the object of improving the measurement accuracy when using field devices with protective tubes in cryogenic applications.

[0013] This object is achieved by the arrangement according to claim 1.

[0014] According to the invention, a device of the arrangement for determining and / or monitoring at least one process variable of a medium in a container of the arrangement comprises a protective tube comprising a tubular, in particular cylindrical, element and a measuring insert which serves to determine and / or monitor the process variable and is accommodated in the protective tube, and wherein the tubular element is fastened to the container in such a way that the tubular element protrudes at least partially into an internal volume of the container. According to the invention, the tubular element of the protective tube has an inlet opening and an outlet opening, which inlet opening and outlet opening are arranged on opposite sides of the tubular element.

[0015] The outlet opening is arranged in a first, in particular distal, end region of the tubular element, which first end region faces the medium, and the inlet opening is arranged in a second, in particular proximal, end region of the tubular element, which second end region faces the container.

[0016] It is also conceivable to provide the protective tube with several openings, particularly at different positions. However, the outlet opening is preferably the one furthest from the container wall.

[0017] The inlet and outlet openings are both located in a region of the protective tube that, when inserted into the container, is located inside the container. Thus, the medium can enter and exit the internal volume of the protective tube through these openings. The flow of medium into at least a portion of the internal volume of the protective tube can significantly reduce effects associated with heat conduction.

[0018] The container is, for example, a tank or a pipeline. In the case of a pipeline through which a medium flows, it is advantageous, for example, if the inlet opening, when the protective tube is attached to the pipeline, faces a flow direction of the medium, and if the outlet opening, when the protective tube is attached to the pipeline, faces away from a flow direction of the medium.

[0019] According to the invention, the inlet opening and / or the outlet opening are arranged and / or configured such that the medium flows around the measuring insert when inserted into the tubular element. The flow around the measuring insert within the protective tube leads to improved measurement performance with regard to the determination and / or monitoring of the process variable.

[0020] The protective tube is installed from below into the container in such a way that the inlet opening at the second, particularly proximal, end of the tubular element is located below the outlet opening at the first, particularly distal, end of the tubular element. Due to the installation from below, any gas bubbles that form rise within the protective tube and exit the protective tube through the outlet opening.

[0021] During installation from below, an included angle between the vertical direction and a longitudinal direction pointing from the first, in particular distal, end region to the second, in particular proximal, end region is between 0° and 90°. When inserting the protective tube and / or the device using a receiving nozzle, for example, an angle between a longitudinal axis of the receiving nozzle and an imaginary horizontal line lies in an interval between 0° and -90°. The protective tube and the device are therefore inserted into the container in such a way that, when the protective tube and the first end region of the protective tube and the device are installed, they are at their highest point, relative to an imaginary vertical line.

[0022] The inlet opening is located at the second, particularly proximal, end of the tubular element, below the outlet opening at the first, particularly distal, end of the tubular element. Due to the bottom-mounted installation, any gas bubbles that form in the protective tube rise and exit the protective tube through the outlet opening.

[0023] One embodiment of the invention includes the inlet opening and / or the outlet opening being arranged and / or configured such that, when the tubular element is attached to the container and when the measuring insert is inserted into the tubular element, a predeterminable back pressure prevails in the region of the inlet opening. In this case, the inlet opening therefore forms a stagnation point for the medium. This embodiment is particularly advantageous when using a container in the form of a pipeline. However, back pressure can also occur in the region of the inlet opening in containers, for example, in the case of cryogenic media.

[0024] A design for the protective tube includes that the inlet opening and / or the outlet opening is / are arranged in the region of a lateral surface of the tubular element.

[0025] At least one of the openings can also be located in the region of an end face of the tubular element. This allows the flow to flow around the measuring element from the inlet opening, preferably located in the area of ​​the lateral surface, to the outlet opening located on the end face. Typically, the sensor element of the measuring insert used is located in the region of the end face of the protective tube when the measuring insert is inserted into the protective tube. These measures ensure that the measuring element is not affected by heat dissipation.

[0026] One embodiment includes the tubular element being closed in the region of an end face, which faces the medium when the tubular element is attached to the container. In this case, the outlet opening is arranged in the region of the outer surface of the tubular element.

[0027] However, it is also conceivable for the protective tube, in particular the tubular element, to be open in the region of the end face facing the medium. In this case, it is advantageous if the outlet opening is arranged in the region of the end face facing the medium when the tubular element is attached to the container.

[0028] A further embodiment provides that the end face of the tubular element is chamfered, and that, particularly in the case where the container is a pipeline or a measuring tube, the protective tube can be attached to the container in such a way that the chamfer faces away from the flow direction of the medium when the protective tube is attached to the container. Such a measure can increase the prevailing dynamic pressure.

[0029] Finally, in one embodiment of the arrangement, the protective tube comprises a fastening insert for fastening a thermometer in a pipe socket of a measuring tube, comprising a holding element for fastening the thermometer to the fastening insert, and a locking device which is designed to prevent a rotational movement of the thermometer relative to the measuring tube, wherein the fastening insert is designed and / or arranged such that the fastening insert is movable parallel to a longitudinal axis through the pipe socket. Such a fastening insert serves to avoid adversely affecting vortex-induced vibrations and takes into account in particular the special problems associated with applications at low temperatures, such as different thermal expansion coefficients of the various components of the thermometer or heat conduction effects. In this context, reference is made to the previously unpublished German patent application with the file number 102020109424.8 referred to.

[0030] The device of the arrangement according to the invention is, for example, a field device with a sensor unit and electronics. In particular, it is a thermometer for determining and / or monitoring temperature with a temperature sensor, for example in the form of a resistance element or thermocouple.

[0031] In a further embodiment of the arrangement, the protective tube and / or the device is / are designed such that the protective tube and / or the device can be fastened in a receiving nozzle of the container.

[0032] In the case of a container in the form of a pipeline, it is advantageous in this regard, for example, if the arrangement further comprises a measuring tube for guiding the medium, wherein the measuring tube has a pipeline section and a pipe socket for receiving the device, and wherein a longitudinal axis of the pipe socket has a predeterminable angle, in particular an angle of substantially 90°, to a longitudinal axis of the pipeline section. In this case, the measuring tube is, for example, a T-piece. Alternatively, other configurations for the measuring tube are also conceivable, such as a design in the form of a corner piece.

[0033] The invention is explained in more detail with reference to the following figures. They show: Fig. 1 a thermometer with a protective tube according to the state of the art, Fig. 2 a first embodiment of an arrangement according to the invention with a protective tube closed at the end, Fig. 3 a second embodiment of an arrangement according to the invention with a protective tube open at the end, Fig. 4 a third embodiment of an arrangement according to the invention with a protective tube open at the end and a bevel, Fig. 5 a fourth embodiment of an arrangement according to the invention with a protective tube open at the end and a bevel, and Fig. 6 a schematic representation of the temperature profile with a protective tube according to the invention.

[0034] In the figures, identical elements are provided with the same reference numerals. The following description refers, without limiting the generality of the concept underlying the invention, to measuring arrangements for determining and / or monitoring temperature. Likewise, the following description is limited, by way of example, to the case of a container in the form of a pipeline. It goes without saying, however, that a protective tube according to the invention can also be used with other types of containers.

[0035] Fig. 1 shows an arrangement 1 for determining and / or monitoring the temperature T of a medium M in a pipeline 2, which medium flows through the pipeline 2 at a flow velocity v. The arrangement 1 comprises a device 3 for determining and / or monitoring the temperature T in the form of a thermometer with a measuring insert 4, in which a temperature sensor (not shown separately here) is arranged. The measuring insert 4 is arranged in a protective tube 5, which is introduced into the pipeline 2 by means of a receiving nozzle 6 fastened to the pipeline 2.

[0036] To achieve the highest possible measurement accuracy for applications in the low or cryogenic temperature range, such arrangements are typically shielded from the environment with insulation. Nevertheless, such arrangements result in undesirable heat conduction from the environment to the measuring element. The mounting units, usually made of metal, for attaching the thermometer 3 to the pipe 2 play a crucial role here. Accordingly, the measured temperature value is usually too high.

[0037] In applications involving cryogenic temperatures, gas bubbles also form due to partial evaporation of the medium due to the large temperature differences between the measuring insert and the medium. These gas bubbles rise to the top and collect in the interior volume of the receiving nozzle. The nozzle then receives less or no liquid medium flow, causing further undesirable heat input during temperature determination using the measuring insert.

[0038] Such problems can be solved by means of an arrangement 1 according to the invention with a protective tube 5 according to the invention. A first embodiment of an arrangement 1 with a protective tube 5 according to the invention is shown in Fig. 2 shown.

[0039] The protective tube 5 comprises a tubular element 7 with an inlet opening 8 and an outlet opening 9, which are arranged on opposite sides of the tubular element 7. In this exemplary embodiment, the inlet opening 7 faces the flow v of the medium M; the outlet opening 8 faces away from the flow v. The tubular element 7 is closed at the end s and the two openings 8, 9 are arranged in the region of the lateral surface m of the tubular element 7. The inlet opening 8 is introduced in a region facing a wall of the pipeline 2, while the outlet opening 9 is arranged in a region facing the medium M or the end face s. In the region of the inlet opening 8, a dynamic pressure p is created, resulting in a pressure difference within the protective tube 5.Forced convection is achieved, resulting in a flow through the internal volume of the protective tube 5 and the measuring insert 4. This effectively dissipates heat introduced into the process from the outside. This, in turn, leads to significantly increased measurement accuracy.

[0040] By installing from below, i.e. with an angle of essentially 90° between an imaginary horizontal line and a longitudinal axis of the mounting nozzle 6 or protective tube 4, so that an included angle between the vertical direction and a longitudinal direction of the protective tube 5 pointing from the first end region to the second end region is essentially 0°, any gas bubbles that form can rise and exit the protective tube 5 through the outlet opening 9. The resulting evaporation processes have even higher heat transfer coefficients than the forced convection of the medium. The removal of the gas bubbles thus causes highly effective cooling of the measuring insert. Ideally, adverse effects of heat introduced by the environment can be essentially completely avoided because pressure and temperature are directly linked via the vapor pressure curve.This measure therefore ensures a further increase in the measurement accuracy when determining temperature.

[0041] A further exemplary embodiment of an arrangement 1 according to the invention is shown in Fig. 3 In contrast to the Fig. 2 shown design is in the case of Fig. 3 the tubular element 7, i.e. the protective tube 5, is open in the area of ​​the end face s and the measuring insert 4 protrudes from the protective tube 5, as an example in the design shown here. The measuring insert 4 is thus longer than the protective tube 5. The outlet opening 9 is therefore located in the area of ​​the end face s. In addition, the protective tube 5 has two inlet openings 8a, 8b. The second inlet opening 8b is located in the area of ​​an internal volume of the receiving nozzle 6 when inserted into the pipeline 2. This further reduces negative effects caused by gas bubbles.

[0042] Because the measuring insert 4 protrudes from the protective tube 5, the measuring insert 4, particularly in the area where the temperature sensor is located, is directly surrounded by the flowing medium M. This measure also increases the measuring accuracy of an arrangement according to the invention.

[0043] To avoid vortex-induced vibrations, the arrangement 1 further comprises a fastening insert 10. This comprises at least one opening (not shown here) so that the medium M can flow through the inner volume of the protective tube 5 and leave the protective tube 5 through the outlet opening 9.

[0044] When designing according to Fig.4 the end face s is also chamfered, with the chamfer facing away from the medium M. Installation at an angle between the vertical direction and the longitudinal direction pointing from the first end region to the second end region other than 0°, as is the case for the previous figures, is also possible. Such a configuration is shown, for example, in Fig. 5 illustrated. Furthermore, instead of a T-shaped arrangement, an arrangement in the form of a corner piece can also be realized. Finally, it should also be noted that other configurations can also have more than one outlet opening 9.

[0045] In Fig. 6 Finally, Figure 3 is a schematic representation of a temperature profile T(x) as a function of the position along the longitudinal axis for a vertical installation of the device 3 with the protective tube 5, as in Fig. 4 shown, shown. In Fig. 4 A vertical line is visible, which assigns the areas a, b, and c of the temperature profile to corresponding areas of the arrangement 1. Area a refers to the area of ​​the receiving nozzle 6, i.e., the area of ​​the process connection. Area b refers to the area inside the protective tube 5, and area c refers to the area facing the medium M, in particular the area in which the measuring insert 4 protrudes from the protective tube 5.

[0046] While in region a the temperature profile is dominated by heat conduction within the process connection, in region b cooling occurs through convection and evaporation. In region c, the temperature profile is almost independent of the exact position x, and the temperature T measured by thermometer 3 essentially corresponds to the temperature of the medium M. Bezugszeichen

[0047] 1 Arrangement 2 Pipeline 3 Device for determining and / or monitoring a process variable 4 Measuring insert 5 Protective tube 6 Receptacle 7 Tubular element 8 Inlet opening 9 Outlet opening 10 Mounting insert M Medium T Temperature v Flow velocity x Position along a vertical axis through the arrangement a,b,c different areas of the arrangement

Claims

1. An arrangement, comprising - a device (3) for determining and / or monitoring at least one process variable (T) of a medium (M) in a container (2) with a protective tube (5), said protective tube (5) comprising a tubular, in particular cylindrical, element (7), and with a measuring insert (4), which is used to determine and / or monitor the process variable and is mounted in the protective tube (5), - and a container (2) with a medium (M) arranged inside it, wherein the tubular element (7) is attached to the container (2) in such a way that the tubular element (7) at least partially protrudes into an internal volume of the container (2), wherein the tubular element (7) has an inlet opening (8) and an outlet opening (9), said inlet opening (8) and outlet opening (9) being arranged on opposite sides of the tubular element (7), wherein the inlet opening (8) and / or the outlet opening (9) is / are arranged and / or configured in such a way that the medium (M) flows around the measuring insert (4), wherein the outlet opening (9) is arranged in a first end area of the tubular element (7), said first end area facing toward the medium, wherein the inlet opening (8) is arranged in a second end area of the tubular element (7), said second end area facing toward the container, characterized in that the protective tube (5) is installed in the container (2) from below in such a way that an included angle between the vertical direction and a longitudinal direction of the protective tube (5) extending from the first end area to the second end area is between 0° and 90°, so that the inlet opening (8) at the second, in particular proximal, end area of the tubular element (7) is arranged below the outlet opening (9) at the first, in particular distal, end area of the tubular element (7), so that any gas bubbles produced rise in the protective tube (5) and escape from the protective tube (5) through the outlet opening (9).

2. The arrangement as claimed in claim 1, wherein the inlet opening (8) and / or the outlet opening (9) is / are arranged and / or configured in such a way that there is a specifiable back pressure (p) in the area of the inlet opening (8).

3. The arrangement as claimed in at least one of the preceding claims, wherein the inlet opening (8) and / or the outlet opening (9) is / are arranged in the area of an outer surface (m) of the tubular element (7).

4. The arrangement as claimed in at least one of the preceding claims, wherein the tubular element (7) is sealed in the area of an end face (s) arranged in the first, in particular distal, end area.

5. The arrangement as claimed in at least one of claims 1 to 3, wherein the outlet opening (9) is arranged in the area of the end face (s).

6. The arrangement as claimed in claim 4 or 5, wherein the end face (s) of the tubular element (7) is angled and, in the event that the container (2) is a pipeline or a measuring tube (2), the protective tube (5) is attached to the container (2) in such a way that the angled end face (s) of the protective tube (5) faces away from a flow direction (v) of the medium (M).

7. The arrangement as claimed in claim 1, wherein the container is a pipeline or measuring tube through which a medium flows and - the inlet opening (8) faces toward a flow direction (v) of the medium, and - the outlet opening faces away from the flow direction (v) of the medium.

8. The arrangement as claimed in at least one of the preceding claims, comprising a mounting insert (10) for mounting a thermometer (3) in a tube adapter (6) of a measuring tube, comprising a retaining element for mounting the thermometer (3) using the mounting insert, and a locking mechanism, which is configured to prevent a rotational movement of the thermometer (3) relative to the measuring tube, wherein the mounting insert (10) is configured and / or arranged in such a way that the mounting insert (10) can be moved through the tube adapter (6) parallel to a longitudinal axis of the tube adapter.

9. The arrangement as claimed in claim 1, wherein the protective tube (5) and / or the device (3) is / are attached to the container (2) using a mounting adapter (6) of the container (2).

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